
Legna123 |

A bit old, but Undead Revisited (2011 I think) Said in the Lich Entry of Ecology:
Whether a wizard, a cleric, or another who has deliberately achieved undeath through one means or another, the lich is a creature held together by powerful magic. The magic of the lich staves off the effects of death and prevents the rotting of its flesh, but does little to protect the flesh from desiccation. Once the lich forsakes the pleasures of food and drink, its body loses the nourishment necessary to keep skin strong and supple, and soon the skin and muscles contract, snap, and wither. Fortunately, the lich does not need these to move; its flesh is mere decoration. Even when dealt a blow that would cripple a mortal, the lich has no fear of immobility, for its magical state keeps it fully ambulatory even on broken bones, as if its skeletal structure were held within a frame of invisible forces.
So like LordKailas said, the magic of the ritual doesn't make them rotting, forgetting to eat does.